1. Field of the Invention
The invention relates to a solar cell lead wire, in particular, to a solar cell lead wire with a high cell crack suppressing effect and a method of manufacturing the same.
2. Related Art
In a solar cell, polycrystalline and single crystal Si cells are used as a semiconductor substrate.
As shown in FIGS. 6A and 6B, a solar cell 100 is manufactured by soldering solar cell lead wires 103a and 103b to a predetermined region of a semiconductor substrate 102, i.e., to a front surface electrode 104 provided on a front surface of the semiconductor substrate 102 and to a back surface electrode 105 provided on a back surface thereof. Electricity generated in the semiconductor substrate 102 is transmitted to the outside through a solar cell lead wire 103.
As shown in FIG. 7, a conventional solar cell lead wire 103 is provided with a ribbon-shaped conductive material 112 and molten solder plated layers 113 each formed on an upper surface 112a and a lower surface 112b of the ribbon-shaped conductive material 112. The ribbon-shaped conductive material 112 is formed by, e.g., roll processing a circular cross-section conductor into a ribbon shape, which is called a rectangular conductor or a rectangular wire.
The molten solder plated layer 113 is formed by supplying a molten solder on upper and lower surfaces of the ribbon-shaped conductive material 112 using a hot-dip plating method.
The hot-dip plating method is a method in which the upper surface 112a and the lower surface 112b of the ribbon-shaped conductive material 112 are cleaned by acid pickling, etc., and a solder is laminated on the upper surface 112a and the lower surface 112b of the ribbon-shaped conductive material 112 by passing the ribbon-shaped conductive material 112 through a molten solder bath. As shown in FIG. 7, the molten solder plated layer 113 is formed in a shape bulging from a side portion in a width direction to a center portion, so-called a mountain-like shape, by an effect of surface tension at the time of solidification of the molten solder adhered on the upper surface 112a and the lower surface 112b of the ribbon-shaped conductive material 112 (e.g., JP-A-2002-263880).
In the conventional solar cell lead wire 103 shown in FIG. 7, since the molten solder plated layer 113 bulged in a mountain-like shape is formed on the upper surface 112a and the lower surface 112b of the ribbon-shaped conductive material 112, it is possible to increase spread of the molten solder on the upper surface 112a and the lower surface 112b of the ribbon-shaped conductive material 112, thus, there is an advantage in that joint force is strengthened when soldering to the front surface electrode 104 or the back surface electrode 105 of the semiconductor substrate 102.
However, since the molten solder plated layer 113 of the solar cell lead wire 103 is bulged in a mountain-like shape, it is difficult to obtain a stable laminated state at the time of winding on a bobbin and deformation of the winding is likely to occur. The solar cell lead wire 103 may be tangled due to the deformation of the winding, and may not be pulled out.
The solar cell lead wire 103 is cut to a predetermined length, is sucked up by air suction and moved onto the front surface electrode 104 of the semiconductor substrate 102 of FIG. 6, and is soldered to the front surface electrode 104 of the semiconductor substrate 102. An electrode band (not shown) electrically conducting with the front surface electrode 104 is preliminarily formed on the front surface electrode 104. The molten solder plated layer 113 of the solar cell lead wire 103a is placed in contact with the front surface electrode 104, then, soldering is carried out in this state. The soldering of the solar cell lead wire 103b to the back surface electrode 105 of the semiconductor substrate 102 is carried out in the same way.
At this time, since the molten solder plated layer 113 of the solar cell lead wire 103a of FIG. 7 is bulged and the thickness is uneven, a contact area thereof with the an air suction jig is small and a suction force is not sufficient, hence, there is a problem of a fall during the moving operation.
In addition, a contact area of the front surface electrode 104 with the molten solder plated layer 113 becomes small. When the contact area of the front surface electrode 104 with the molten solder plated layer 113 is small, heat conduction from the semiconductor substrate 102 to the molten solder plated layer 113 is not sufficient, which results in generation of a soldering defect.
In addition, the small contact area of the front surface electrode 104 with the molten solder plated layer 113 causes a misalignment between the solar cell lead wire 103a soldered to the front surface electrode 104 and the solar cell lead wire 103b soldered to the back surface electrode 105 when jointing the solar cell lead wires 103a and 103b to both the front and back surfaces of the semiconductor substrate 102, and a cell crack (which means that the semiconductor substrate 102 is cracked) occurs due to the misalignment. Since the semiconductor substrate 102 is expensive, a cell crack is unfavorable.